Brian Ash (Anthony Andrews) is a young lieutenant who is assigned to a UXB unit in the early days of World War II. UXB (UneXploded Bomb) is the signal that an aerial bomb has not exploded. Ash's job is to deactivate German bombs, some of which have fuses specifically designed to kill him. The series takes us through his maturation as an officer, a love story with Susan (Judy Geeson), and the stresses and strains of wartime on the civilians and military in England.